1. Field of the Invention
The present invention relates to a local plating apparatus, and more particularly, to a local plating apparatus for forming by plating contacts or electrodes, such as bumps for connecting inner leads to a semiconductor chip in tape automated bonding (TAB), on part of a component of an electronic device.
2. Description of the Related Art
FIG. 7 is a cross-sectional view illustrating a conventional local plating method of forming an electric terminal which is disclosed in, for example, Japanese Patent Publication No. 60-45278.
As can be seen in FIG. 7, a material 2 to be plated, such as an electric terminal, is provided on a cathode 1. A mask 3 is provided around the material 2 to be plated. A nozzle 5 for forming a jet 4a of plating solution is disposed in opposed relation to the material 2 to be plated.
In such a conventional jet type local plating technique, a jet 4a of plating solution is ejected to a desired site to be plated by application of a voltage between the cathode 1 and an anode (not shown). Therefore, a high-speed local plating can be performed without performing masking for each material 2 to be plated.
FIG. 8 illustrates a conventional laser-enhanced local plating method which is disclosed in, for example, Japanese Patent Publication No. 59-1797.
As shown in FIG. 8, a plating solution 4 is filled in a container 7 made of a material which passes through a laser beam 6, such as quartz. A material 8 to be plated which is made of glass, serving as a cathode, and an anode 9 are immersed in the plating solution 4 in such a manner that they oppose each other. The material 8 to be plated has a metal layer 10 formed on the surface thereof. The material 8 to be plated and the anode 9 are respectively connected to a power source 11 and a voltage modulater 12.
Outside of the container 7 are provided an energy source 13, such as a laser beam oscillator, a laser modulater 14, a lens 15 and a scanning mirror 16.
The laser beam 6 generated by the energy source 13 is passed through the laser modulater 14, and is then converged by the lens 15. After being positioned by the scanning mirror 16, the laser beam 6 passes through the container 7 and then reaches the material 8 to be plated. The laser beam 6 passes through the material 8 to be plated which is made of glass also, and is focused on the metal layer 10. The material 8 to be plated is charged to a negative polarity by the power source 11, by which electrolytic plating is conducted. At that time, since the metal layer 10 formed on the material 8 to be plated is locally heated to a high temperature by irradiation of the laser beam 6, the speed of plating is increased. Furthermore, fine local plating on the order of a micron is possible without performing masking on the material 8 to be plated.
In the aforementioned conventional jet type plating method which does not employ a laser, a particulate film is readily formed, and cracks are readily generated in an interface between the plated film and the material 2 to be plated. In the aforementioned conventional laser-enhanced plating method, although the position of the portion to be plated is determined by the scanning mirror 16, positioning accuracy of scanning is not high. Consequently, the laser beam 6 may be unfocused or the angle of incidence of the laser beam 6 relative to the metal layer 10 may be varied, thus varying the power density of the laser beam which irradiates the metal layer 10 or the laser absorption coefficient of the metal layer 10. These may generate variations in the quality of plating.
A conventional laser-enhanced jet plating method proposed to improve the jet plating method will be described below. FIG. 9 is a cross-sectional view illustrating the conventional laser-enhanced jet plating method which has been proposed in "Electrochemical Science and Technology" by J. Electrochem. Soc. Vol. 132, from pp 575 to 2581 published in November 1985.
As shown in FIG. 9, a plating tank 17 having a nozzle 5 is made of quartz which passes through a laser beam 6. An anode 9 is provided in the plating tank 17. The plating tank 17 also has an air blender 18 and a plating solution feeding portion 19. Outside of the plating tank 17 is provided a lens 15 which focuses the laser beam 6 to the vicinity of the nozzle 5 in the plating solution 4.
In this method, the jet 4a of plating solution 4 is ejected to the portion to be plated by application of a voltage between the anode 9 and the cathode 1 while the laser beam 6 is focused into the plating solution 4. Due to a difference in the refractivity between the plating solution 4 and the ambient atmosphere, the irradiated laser beam 6 is totally reflected within the jet 4a and thereby reaches the portion of the material 2 to be plated. Since the material 2 to be plated which is irradiated with the laser beam 6 is partially heated to a high temperature, the speed of plating is increased, and a fine film can be plated.
In the aforementioned laser enhanced jet plating method, when the jet 4a is turbulent, total reflection of the laser beam 6 within the jet 4a does not occur, varying the laser output which reaches the portion to be plated. Consequently, variations in the plating quality are generated.